This application is based on Japanese Patent Application No. 10-377652 (1998) filed Dec. 29, 1998 and Japanese Patent Application No. 11-120723 (1999) filed Apr. 27, 1999, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a liquid-ejecting head and a method of ejecting a liquid using such a liquid-ejecting head. The present invention also relates to a liquid-ejecting type printing apparatus using such a liquid-ejecting head or such a method.
2. Description of the Related Art
A liquid-ejecting printing method, which is of forming an image by depositing an ejected liquid on a printing medium using a thermal energy, allows a printing operation at high resolution and high speed with a low noise level and provides a high printing quality. In addition, such a method has advantages that it can be easily applied on a multi-color printing and also it is able to print any information on a piece of ordinary paper.
The liquid-ejecting printing method is disclosed, for example in Japanese Patent Application Laying-open No. 4-10941 (1992) that suggests the process for releasing a bubble into the atmosphere under the condition that the primary product of differentiating a velocity of the bubble that moves on the tip in the direction of eject is defined takes on a negative value. In this case, the work done by the bubble relative to the electric energy applied on a thermal resistor element (which is responsible for generating a thermal energy for ejecting ink from an orifice) is more excellent than that of the former liquid-ejecting head because of the short distance between the thermal resistor element and the orifice. In addition, there is another advantage of stabilizing the volumes of the ejected liquid droplets because the whole volume of the liquid existed between the thermal resistor element and thee orifice can be substantially ejected.
However, the above conventional method includes the following problems to be solved.
It is very difficult to perfectly prevent the generation of splash or mist of the liquid droplet even though the following fact. That is, there is an advantage of substantially preventing the deterioration of printing quality as a result of reducing the generation of splash or mist of the liquid droplet by releasing a bubble into the atmosphere under the condition that the primary product of differentiating a velocity of the bubble that moves on the tip in the direction of ejecting is defined takes on a negative value.
It is also difficult to maintain the printing quality at high level if the following fact is occurred. In the conventional liquid-ejecting method, there is a possibility that a bubble may communicate with the atmosphere through the portion in the vicinity of the orifice on the liquid chamber""s side at first because of the momentary formation of a liquid column at a central portion of the orifice at the time of ejecting the liquid droplet. In this case, the posterior portion of the liquid column hear the above communicating portion may fall on a substrate. On the other hand, a liquid membrane is formed between the remaining posterior portion of the liquid column and the orifice, so that the remaining posterior portion of the liquid column is kept from a drop on the substrate by such a membrane. Consequently, the tail end of the liquid column may falls on the substrate with a deviation from the center of the orifice, resulting in a deleterious effect on the direction along which the liquid droplet flies in straight. Furthermore, it may affect on the accuracy of placing the liquid droplet in the right place In this case, therefore, it is difficult to maintain the printing quality at high level.
For the liquid-ejecting method, one of very important problems is the efforts on further improvement of the image quality by preventing the generation of splash or mist of the liquid droplet to the limit. And other one of very important problems is how to keeping the printing quality at high level by improvement on the accuracy of placing the ink droplet in the right place.
The present invention is implemented to solve the foregoing problems. It is therefore an object of the present invention is to provide a liquid-ejecting head, a method of ejecting a liquid droplet, and a liquid-ejecting printing apparatus that allow the high quality of printing by substantially stabilizing the properties of ejected ink droplets, such as their volumes and flying velocities and their correct positioning, without the generation of splash or mist thereof.
In the first aspect of the present invention, there is provided a liquid-ejecting head comprising:
an orifice plate with an orifice for ejecting liquid;
a substrate provided substantially in parallel to the orifice plate and having energy-generating means for generating thermal energy to be used for generating a bubble to eject liquid from the orifice,
a liquid-flowing path formed between the orifice plate and the substrate and communicated with the orifice so as to supply liquid from a liquid chamber to the orifice, wherein the energy-generating means generates the bubble for forming a flow of liquid that directs to the liquid chamber and a flow of liquid that directs to the orifice in a flow area shifted to a side of the liquid chamber so that an amount of liquid directing to the orifice becomes substantially uniform around an inner peripheral surface of the orifice at a time of ejecting liquid.
Here, a method of ejecting liquid by using the liquid-ejecting head of the first aspect, may comprise the steps of:
deforming a part of the interface between liquid and the bubble formed in liquid so that the interface contacts to the substrate; and
communicating the bubble with an atmosphere after the step of deforming the interface.
A liquid-ejecting printing apparatus for printing, an image on a printing medium by using the liquid-ejecting head of the first aspect, may comprise:
means for moving the liquid-ejecting head and the printing medium relatively to each other; and
means for supplying a driving signal to the liquid-ejecting head.
In the second aspect of the present invention, there is provided a liquid-ejecting head comprising:
an orifice plate with an orifice for ejecting liquid;
a substrate provided substantially in parallel to the orifice plate and having energy-generating means for generating thermal energy to be used for generating a bubble to eject liquid from the orifice,
a liquid-flowing path formed between the orifice plate and the substrate and communicated with the orifice so as to supply liquid from a liquid chamber to the orifice, wherein
the energy-generating means generates the bubble for forming a flow of liquid that directs to the liquid chamber and a flow of liquid that directs to the orifice in a flow area shifted to a side of the liquid chamber so that a thickness of a liquid membrane is uniformly formed along an inner peripheral surface of the orifice at the time of ejecting the liquid.
Here, a method of ejecting liquid by using the liquid-ejecting head of the second aspect, may comprise the steps of:
deforming a part of the interface between liquid and the bubble formed in liquid so that the interface contacts to the substrate; and
communicating the bubble with an atmosphere after the step of deforming the interface.
A liquid-ejecting printing apparatus for printing an image on a printing medium by using the liquid-ejecting head of the second aspect, may comprise:
means for moving the liquid-ejecting head and the printing medium relatively to each other; and
means for supplying a driving signal to the liquid-ejecting head.
In the third aspect of the present invention, there is provided a liquid-ejecting head comprising:
an orifice plate with an orifice for ejecting liquid;
a substrate provided substantially in parallel to the orifice plate and having energy-generating means for generating thermal energy to be used for generating a bubble to eject liquid from the orifice,
a liquid-flowing path formed between the orifice plate and the substrate and communicated with the orifice so as to supply liquid from a liquid chamber to the orifice, wherein
a shape of a cross section of the orifice in parallel with the substrate which is projected on the substrate from a side of the orifice plate is composed of a partial combination of a plurality of figures and a centroid of the cross section and a centroid of the energy-generating means are coincident with each other.
Here, a method of ejecting liquid by using the liquid ejecting head of the third aspect, may comprise the steps of:
deforming a part of the interface between liquid and the bubble formed in liquid so that the interface contacts to the substrate; and
communicating the bubble with an atmosphere after the step of deforming the interface.
A method of ejecting liquid by using the liquid-ejecting head of the third aspect, may comprise the step of:
generating a bubble using the energy-generating means that generates the bubble for forming a flow of liquid that directs to the orifice so that a thickness of a liquid membrane is uniformly formed along an inner peripheral portion of the orifice at the time of ejecting the liquid.
A liquid-ejecting printing apparatus for printing an image on a printing medium by using the liquid-ejecting head of the third aspect, may comprise:
means for moving the liquid-ejecting head and the printing medium relatively to each other; and
means-for supplying a driving signal to the liquid-ejecting head.
In the fourth aspect of the present invention, there is provided a liquid-ejecting head comprising:
an orifice plate with an orifice for ejecting liquid;
a substrate provided substantially in parallel to the orifice plate and having energy-generating means for generating thermal energy to be used for generating a bubble to eject liquid from the orifice,
a liquid-flowing path formed between the orifice plate and the substrate and communicated with the orifice so as to; supply liquid from a liquid chamber to the orifice, wherein
a contour of a cross section of the orifice in parallel with the substrate which is projected on the substrate from a side of the orifice plate is composed of a partial combination of contours of a plurality of figures and a centroid of the cross section and a centroid of the energy-generating means are coincident with each other.
Here, a method of ejecting liquid by using the liquid-ejecting head of the fourth aspect, may comprise the steps of:
deforming a part of the interface between liquid and the bubble formed in liquid so that the interface contacts to the substrate; and
communicating the bubble with an atmosphere after the step of deforming the interface.
A method of ejecting liquid by using the liquid-ejecting head of the fourth aspect, may comprise the step of:
generating a bubble using the energy-generating means that generates the bubble for forming a flow of liquid that directs to the orifice so that a thickness of a liquid membrane is uniformly formed along an inner peripheral portion of the orifice at the time of ejecting the liquid.
A liquid-ejecting printing apparatus for printing an image on a printing medium by using the liquid-ejecting head of the fourth aspect, may comprise:
means for moving the liquid-ejecting head and the printing medium relatively to each other; and
means for supplying a driving signal to the liquid-ejecting head.
According to the present invention, therefore, the following items (1) and (2) can be successively attained with stability.
(1) Under the condition that a bubble and the atmosphere are not communicated with each other, a posterior end of liquid column as a part of the interface between the bubble and the liquid comes into contact with a substrate that forms a part of a liquid-flowing path without causing any deviation from a central axis of an orifice. Thus, the property of keeping the liquid column as a straight line and the property of keeping the direction along which a liquid droplet flies in straight are attained.
(2) After the contact between the posterior end of the liquid column and the substrate, the air babble communicates with the atmosphere at a portion of the inner side of the orifice in the vicinity of the substrate. Thus, the release of splash or mist of the liquid to the outside of the liquid-flowing path can be prevented. In addition, a cavitation damage can be also prevented.
By successively satisfying the above items (1) and (2), the deterioration of an image quality of the printed image caused by unstable satellite can be prevented. Because, the properties of ejected liquid droplets, such as their volumes and flying velocities and also the behavior of the tail end of the liquid droplet at the time of running out of the liquid are substantially stabilized. Furthermore, the high quality image can be allowed as a result of preventing the generation of mist by performing the communication between the bubble and the atmosphere in the liquid-flowing path.
Some of the current-used methods for manufacturing the conventional liquid-ejecting heads may be applicable to a liquid-ejecting head of the present invention. Using the liquid-ejecting head of the present invention, a novel method for ejecting a liquid can be realized. The novel method comprises the steps of deforming a part of the interface between a liquid and a bubble formed in the liquid; land communicating the bubble with the atmosphere. According to the present invention, furthermore, there is no need to increase the number of manufacturing steps in the novel method, so that the effective cost for production can be attained.
Accordingly, the present invention allows the stable eject of liquid droplets by stabilizing the conditions of ejecting liquid droplets and also stabilizing the behavior of the tail end of the liquid droplet at the time of running out of the liquid. If an image is formed using such liquid droplets, the deterioration of image quality of the printed image caused by unstable satellite can be prevented. In addition, the printing of image at high quality can be allowed as a result of preventing the generation of mist by performing the communication between the bubble and the atmosphere in the liquid-flowing path.
In the present invention, furthermore, there is no step of the collapse of a bubble, so that we can prevent any damage on a means of generating energies, such as a heater, by cavitation (i.e., the sudden formation and collapse of air bubbles in the liquid). Accordingly, the longevity of the liquid-ejecting head can be increased.
Furthermore, some of the currently-used methods for manufacturing the conventional liquid-ejecting heads may be applicable to a liquid-ejecting head of the present invention, so that there is no need to increase the number of manufacturing steps in the novel method and thus the effective cost for production can be attained.